Method and apparatus for generating a self-correcting local oscillation

ABSTRACT

A method and apparatus for generating a self-correcting local oscillation includes processing that begins by generating a synthesized frequency from a reference frequency. The processing then continues by dividing the synthesized frequency by a divider value to produce a divided frequency. The processing continues by generating an auxiliary frequency and mixing the auxiliary frequency with the divided frequency to produce a corrected frequency. The processing then continues by mixing the corrected frequency with the synthesized frequency to produce a local oscillation.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to wireless communications and moreparticularly to generating a local oscillation for use within wirelessradio devices.

BACKGROUND OF THE INVENTION

As is known, in-home/in-building networks and point-to-point wirelesscommunications occur between two or more wireless communication devicessuch as laptop computers, personal computers, personal digitalassistants, Internet connections, hand held radios, et cetera. Suchwireless communication devices include a transmitter section and areceiver section. In general, the transmitting section includes amodulator, an up-conversion intermediate frequency (IF) stage, and apower amplifier to drive an antenna. The receiving section generallyincludes a low noise amplifier operably coupled to an antenna, adown-conversion IF stage, and a demodulator.

To transmit data from one wireless communication device to another, themodulator of the transmitting section of the initiating device modulatesthe data to produce modulated data. The up-conversion IF stage mixes themodulated data with a local oscillation to produce an RF signal that isamplified by the power amplifier and transmitted via the antenna. Alocal oscillator generates the local oscillation from a crystaloscillator circuit within the initiating device.

The receiving section of the targeted device receives, via its antenna,the RF signal, which is amplified by the low noise amplifier. The RFsignal is then mixed with a local oscillation via the down-conversion IFstage to produce an IF signal or base-band signal. The demodulatordemodulates the IF signal or base-band signal to recapture the data. Alocal oscillator in the receiving section of the receiving devicegenerates the local oscillation that is used for the down conversion ofthe RF signal. The particular modulation scheme and subsequentdemodulation scheme used by the initiating device and targeted device isdependent on the particular wireless communication protocol adhered toby such devices. For example, the wireless communication protocol may beBluetooth, IEEE 802.11a, IEEE 802.11b, code division multiple access(CDMA), analog mobile phone service (AMPS), digital AMPS, global systemfor mobile (GSM), wireless application protocol (WAP) and/or any otherwireless communication standard.

Typically, the local oscillation used by the receiving section andtransmitting section in each wireless communication device is derivedfrom a crystal oscillator and a phase locked loop. Since crystaloscillators are generally inaccurate devices (e.g., have an error of+/−5%), the local oscillation produced by one wireless communicationdevice may not be the same local oscillation as produced by anotherwireless communication device. When this occurs, a DC offset results inthe receiving section of the targeted wireless communication device.Such a DC offset can cause errors in the recapturing of the data. Theerrors caused by the DC offset may be magnified when the wirelesscommunication devices employ complex modulation schemes.

As is further known, in-home/in-building networking and point-to-pointwireless communications are governed by a variety of standards includingBluetooth, IEEE802.11a, IEEE802.11b, et cetera. Each of these standardsprovides guidelines for encoding/decoding and/or modulating/demodulatingdata. In addition, the standards specify a frequency band for thewireless conveyance of data. For example, the IEEE 802.11a standardspecifies a frequency band of 5.15 gigahertz to 5.35 gigahertz and 6.725gigahertz to 5.825 gigahertz and further specifies a modulation schemeof orthogonal frequency division multiplexing (OFDM).

For a wireless communication device to be compliant with the IEEE802.11a standard, it must generate, for a direct down-conversion, alocal oscillation that has a range of 5.18 gigahertz to 5.32 gigahertzand also a range of 5.745 gigahertz to 5.805 gigahertz. In addition, thelocal oscillation should be accurate within a few kilohertz such that itcan be centered in the 16.25 megahertz bandwidth of each channel, whichconsists of 312.5 kilohertz sub-channels. Further, the local oscillationshould be able to change its frequency very quickly to accommodate thechannels. Consequently, a phase locked loop within the local oscillatorcannot be used to adjust the frequency of the local oscillation since itis too slow (e.g., a PLL has a bandwidth of up to 60 kilohertz).

Therefore, a need exists for a method and apparatus of generating aself-correcting local oscillation that is accurate to within a fewkilohertz and may be changed quickly to provide a range of localoscillations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of an integrated radioreceiver in accordance with the present invention;

FIG. 2 illustrates a schematic block diagram of a self-correcting localoscillator in accordance with the present invention;

FIG. 3 illustrates a schematic block diagram of an auxiliary frequencycontrol module in accordance with the present invention;

FIG. 4 illustrates a schematic block diagram of a mixing module inaccordance with the present invention;

FIG. 5 illustrates a schematic block diagram of an integrated radioreceiver in accordance with the present invention;

FIG. 6 illustrates a schematic block diagram of the radio receiver ofFIG. 5 in a test mode in accordance with the present invention;

FIG. 7 illustrates a frequency response of the radio receiver of FIG. 6;

FIG. 8 illustrates a schematic block diagram of an alternateself-correcting local oscillator in accordance with the presentinvention; and

FIGS. 9 through 11 illustrate a logic diagram of generating aself-correcting local oscillation in accordance with the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Generally, the present invention provides a method and apparatus forgenerating a self-correcting local oscillation. Such a method andapparatus includes processing that begins by generating a synthesizedfrequency from a reference frequency. The processing then continues bydividing the synthesized frequency by a divider value to produce adivided frequency. The processing continues by generating an auxiliaryfrequency and mixing the auxiliary frequency with the divided frequencyto produce a corrected frequency. The processing then continues bymixing the corrected frequency with the synthesized frequency to producea local oscillation. With such a method and apparatus, an accuratereadily adjustable local oscillator is achieved.

The present invention can be more fully described with reference toFIGS. 1 through 12. FIG. 1 illustrates a schematic block diagram of anintegrated radio receiver 10 that includes an RF receiving section 12and a self-correcting local oscillator 14. The RF receiver section 12 isoperably coupled to receive an inbound RF signal 16 and a localoscillation 20. From these inputs, the RF receiver section 12 producesan inbound intermediate frequency (IF) signal 18. For example, theinbound RF signal 16 may be modulated in accordance with the IEEE802.11a standard such that it has a frequency range of 5.15 gigahertz to5.35 gigahertz and another range of 5.725 gigahertz to 5.825 gigahertz.Accordingly, the local oscillation 20 will have a frequency range of5.18 gigahertz to 5.32 gigahertz and 5.745 gigahertz to 5.805 gigahertz.The inbound IF signal 18 will be at base-band. A demodulator, which isnot shown, will process the inbound IF signal 18 to retrieve data fromthe modulated data.

The self-correcting local oscillator 14 includes a frequency synthesizer22, a divider module 24, a 1^(st) mixing module 28, a 2^(nd) mixingmodule 30, and an auxiliary frequency control module 26. The frequencysynthesizer 22 generates a synthesized frequency 34 from a referencefrequency 32. For example, a crystal oscillator may generate thereference frequency 32 to have a frequency in the range of 10 to 20megahertz. The frequency synthesizer 22 may be a phase locked loop (PLL)that produces the synthesized frequency 34 to be approximately ⅔ rds thedesired frequency of the local oscillation 20.

In an embodiment, the phase locked loop incorporates a 3^(rd) order mashDelta Sigma modulator to provide fractional divisors that allow for alarge range of reference crystal selections and a wide phase locked loopbandwidth for faster loop locking time and better noise suppression. ThePLL includes a phase/frequency detector, a charge pump, a low passfilter, voltage controlled oscillator that generates the synthesizedfrequency 34 and a multi-modulus divider. The multi-modulus divider,which provides the reference frequency to the phase frequency detector,has its inputs determined by the Delta Sigma modulator and a constantfactor corresponding to the channel selected for transmission of data.

The multi-modulus divider dynamically changes the divisor value based onthe cutput of the Delta Sigma modulator such that the average outputover several reference cycles is the fractional value necessary togenerate the correct output frequency. The multi-modulus divider may beimplemented using 6 stages of divide by ⅔ rds dividers, which provides adivisor range between the values of 64 and 127. Such a divisor rangeallows for a reference crystal range of 16 megahertz to 24 megahertz toproduce the desired synthesized frequency 34 for use in an IEEE 802.11acompliant radio receiver.

The divider module 24 divides the synthesized frequency 34 by a dividervalue 36. Accordingly, the divider module 24 produces a dividedfrequency 38. If the synthesized frequency 34 is generated to be ⅔ rdsof the local oscillation, the divider value 36 will be 2. As such, thedivided frequency 38 will be of half the frequency as that of thesynthesized frequency 34 and ⅓ of the frequency of the localoscillation.

The auxiliary frequency control module 26 generates an auxiliaryfrequency 40 in the 100 kilohertz to 300 kilohertz range. The auxiliaryfrequency control module 26 generates the auxiliary frequency 40 tocompensate for frequency spectrum errors within the local oscillator 14and/or generates the auxiliary frequency based on a fine tuningfrequency selection. The fine tuning of the auxiliary frequency 40allows for the local oscillation 20 to be centered within desiredchannels of an IEEE 802.11a transmission. The details of the auxiliaryfrequency control module 26 will be described in greater detail withreference to FIGS. 3 and 6 through 12.

The 1^(st) mixing module 28 mixes the divided frequency 38 with theauxiliary frequency 40 to produce a corrected frequency 42. If theself-correcting local oscillator 24 is to generate a local oscillation20 for use in an IEEE802.11a compliant radio receiver, the synthesizedfrequency will be in the range of 3.45 gigahertz to 3.87 gigahertz.Accordingly, the divided frequency 38 will be 1.72 gigahertz to 1.94gigahertz. Since the auxiliary frequency 40 is in the range of 100 to afew hundred kilohertz, the corrected frequency 42 is a small fractiongreater than the divided frequency 38.

The 2^(nd) mixing module 30 mixes the synthesized frequency 34, whichhas a frequency that is ⅔ rds of the local oscillation, with thecorrected frequency 42, which has a frequency of approximately ⅓^(rd)the local oscillation. Thus, when the synthesized frequency 34 is summedwith the corrected frequency 42 the local oscillation 20 is produced. Bygenerating the local oscillation 20 from the synthesized frequency andthe divided frequency 38, the affects of the local oscillator pulling onthe phase locked loop output are substantially reduced.

FIG. 2 illustrates a more detail schematic block diagram of theself-correcting local oscillator 14. The local oscillator 14 includesthe frequency synthesizer 22, the divider module 24, the auxiliaryfrequency control module 26, which produces an I component 58 and a Qcomponent 60 of the auxiliary frequency 40, the 1^(st) mixing module 28and the 2^(nd) mixing module 30. The divider module 24 includes a divideby N module 50 and a phase shift module 52. In this embodiment, thedivider module 24 produces an I component 54 and a Q component 56 of thedivided frequency 38.

The 1^(st) mixing module 28 includes a 1^(st) mixer 62, a 2^(nd) mixer64, a 3^(rd) mixer 66, a 4^(th) mixer 68, a 1^(st) summing module 78 anda 2^(nd) summing module 80. The 1^(st) mixer 62 is operably coupled tomix the Q component 56 of the divided frequency 38 with the I component58 of the auxiliary frequency 40 to produce a 1^(st) mixed frequency 70.The 2^(nd) mixer 64 is operably coupled to mix the Q component 56 of thedivided frequency 38 with the Q component 60 of the auxiliary frequency40 to produce a 2^(nd) mixed frequency 72. The 3^(rd) mixer 66 isoperably coupled to mix the I component 54 of the divided frequency 38with the I component 58 of the auxiliary frequency 40 to produce a3^(rd) mixed frequency 74. The 4^(th) mixer 68 is operably coupled tomix the I component 54 of the divided frequency 38 with the Q component60 of the auxiliary frequency 40 to produce a 4^(th) mixed frequency 76.

The 1^(st) summing module 78 is operably coupled to sum the 1^(st) mixedfrequency 70 with the 4^(th) mixed frequency 76 to produce a Q component84 of the corrected frequency 42. The 2^(nd) summing module 80 isoperably coupled to sum the 2^(nd) mixed frequency 72 with the 3^(rd)mixed frequency 74 to produce an I component 82 of the correctedfrequency 42.

While the 1^(st) mixing module 28 allows for mixing of the auxiliaryfrequency 40 into the local oscillation 20, it introduces unwanted tonesdue to the DC offset in the mixers and the phase/gain mismatches of themixers. The DC offset causes a local oscillation feed through tone atapproximately ½ the synthesized frequency and the phase/gain mismatchescreate an unwanted image tone at ½ the synthesized frequency minus theauxiliary frequency. The auxiliary frequency control module 26, as willbe discussed in greater detail with reference to FIGS. 3 and 6 through10, minimizes the affects of these unwanted tones to achieve the desiredbenefits of mixing the auxiliary frequency into the local oscillation.As previously mentioned, by adding the auxiliary frequency into thelocal oscillation, the local oscillation can be finely tuned withaccuracies greater than 0.1%.

The 2^(nd) mixing module 30 includes a 5^(th) mixer 94 and a 6^(th)mixer 96. The 5^(th) mixer 94 is operably coupled to mix the Q component84 of the corrected frequency 42 with a Q component of the synthesizedfrequency 34. The resultant is the Q component 86 of the localoscillation 20. The 6^(th) mixer 96 is operably coupled to mix the Icomponent 82 of the corrected frequency 42 with an I component of thesynthesized frequency 34 to produce an I component 88 of the localoscillation 20.

FIG. 3 illustrates a schematic block diagram of the auxiliary frequencycontrol module 26. The auxiliary frequency control module 26 includes anauxiliary frequency synthesizer 92, a processing module 90, and memory91. The processing module 90 may be a single processing device or aplurality of processing devices. Such a processing device may be amicrocontroller, microcomputer, microprocessor, digital signalprocessor, field programmable gate array, programmable logic device,state machine, logic circuitry, central processing unit, and/or anydevice that manipulates signals (analog and/or digital) based onoperational instructions. The memory 91 may be a single memory device ora plurality of memory devices. Such a memory device may be a read-onlymemory, random access memory, volatile memory, non-volatile memory,static memory, dynamic memory, flash memory, and/or any device thatstores digital information. Note that when the processing module 92implements one or more of its functions via a state machine or logiccircuitry, the memory storing the corresponding operational instructionsis embedded within the circuitry comprising the state machine and/orlogic circuit. The processing module 90 implements one or more of theprocessing steps illustrated in FIGS. 9 through 12.

In general, the processing module 90 generates a frequency correctionsignal 93 to correct for the tones introduced by the mixers within the1^(st) mixing module. In addition, the frequency correction signal 93may include further information to indicate the particular fine tuningrequired of the local oscillation 20.

The processing module 90 may also produce an input selection signal 140,which places the radio receiver 10 in a test mode or normal mode. Theuse of the input selection signal 140 will be described in greaterdetail with reference to FIGS. 5 and 6.

The auxiliary frequency synthesizer 92, which may be a phase lockedloop, direct digital frequency synthesizer, or any other device thatgenerates a sinusoidal reference signal, produces the I component 58 ofthe auxiliary frequency 40 and the Q component 60 of the auxiliaryfrequency 40 based on the frequency correction signal 93.

FIG. 4 illustrates an alternate schematic block diagram of the 1^(st)mixing module 28. The 1^(st) mixing module 28 includes a 1^(st) mixer62, a 2^(nd) mixer 64, and a polyphase filter 100. The 1^(st) mixer 62is operably coupled to mix an I component of the divided frequency 38with an I component 58 of the auxiliary frequency 40. The 1^(st) mixingmodule 62 produces an I component of the mixed frequency 100. The 2^(nd)mixer 64 is operably coupled to mix the divided frequency 38 with a Qcomponent 60 of the auxiliary frequency 40 to produce a Q component 102of the mixed frequency.

The polyphase filter 100, which includes filtering to reject imagesproduces by the 1^(st) and 2^(nd) mixers, generates the I component 82of the corrected frequency 42 and the Q component 84 of the correctedfrequency 42. For a more detailed discussion of the polyphase filter100, refer to co-pending Patent Application entitled Adaptive RadioTransceiver with Filtering, having a Ser. No. 09/692,420, a filing dateof Oct. 19, 2000 and is assigned to the same Assignee as the presentapplication.

FIG. 5 illustrates a schematic block diagram of the radio receiver 10 toinclude the 4 mixers 62 through 64 of the 1^(st) mixing module 28, the1^(st) and 2^(nd) summing modules 78 and 80 of the 1^(st) mixing module,the 5^(th) and 6^(th) mixers 94 and 96 of the 2^(nd) mixing module 30,the RF receiver section 12, an input selection switch 136 and an adder138. The functionality of the 1^(st) and 2^(nd) mixing modules 28 and 30are as previously discussed to produce the I and Q components 88 and 86of the local oscillation 20.

The RF receiver section 12 includes a 7^(th) mixer 110, an 8^(th) mixer112, a high-pass filter 114, a high-pass filter 116, an analog todigital converter 118, and an analog to digital converter 120. The7^(th) mixer 110 is operably coupled to mix the Q component 86 of thelocal oscillation 20 with either the output of adder 138 or the inboundRF signal 122. The particular input provided to the 7^(th) mixer 110 isbased on the input selection signal 140. For normal operations, theinput selection signal 140 causes the input selection switch 136, whichmay be a physical switch, a logical switch, and/or combination thereof,to couple the input RF signal 122 to the 7^(th) and 8^(th) mixers 110and 112. During test mode, the input selection signal 140 causes thesummed local oscillation 142 to be provided to the 7^(th) and 8^(th)mixers 110 and 112. The test mode will be described in greater detailwith reference to FIG. 6.

When the inbound RF signal 122 is coupled to the 7^(th) and 8^(th)mixers, the functionality of the RF section 12 produces the digital Ibase-band signal 134 and digital Q base-band signal 132. In operation,the 7^(th) mixer 110 mixes the Q component of local oscillation 20 witha Q component of the inbound RF signal 122 to produce a Q component ofbase-band signal 124. The high-pass filter 114 filters the Q componentof base-band signal 124 to produce a filtered Q base-band signal 128.The analog to digital converter 118 converts the filtered Q base-bandsignal 128 into the digital Q base-band signal 132. Similarly, the8^(th) mixer 112 mixes an I component of local oscillation 20 with an Icomponent of the inbound RF signal 122 to produce an I component ofbase-band signal 126. The high pass filter 116 filters the I componentof the base-band signal 126 to produce a filtered I base-band signal130. The analog to digital converter 120 converts the filtered Ibase-band signal 130 into the digital I base-band signal 134.

FIG. 6 illustrates the radio receiver 10 being configured for test mode.In this configuration, the processing module 90 generates the inputselection signal 140 to couple the output of summing module 138 to the7^(th) and 8^(th) mixers 110 and 112. As is further illustrated in FIG.6, various signals are identified by letters A through G. The frequencyresponse for each of these signals is illustrated in FIG. 7.Accordingly, the discussion with respect to FIG. 6 will also include adiscussion with respect to FIG. 7. In this configuration, the voltagecontrolled oscillator 152 generates a reference frequency 32, which hasa designation of A:f_(vco). Referring to FIG. 7, the reference frequency32 has a frequency response at the frequency of the voltage controlledoscillator. For example, if the radio receiver 10 is constructed to becompliant with IEEE 802.11a, the frequency produced by the voltagecontrol oscillator will be in the range of 3.45 gigahertz to 3.87gigahertz.

The divide by 2 module 150 receives the reference frequency 32 andproduces an I and Q component of a divided frequency. The dividedfrequency is referenced as B:f_(vco)/2. Referring to FIG. 7, the dividedfrequency 38 has a frequency at ½ that of the voltage controlledoscillator.

The auxiliary frequency synthesizer 92 based on the frequency correctionsignal 93, which will be discussed in greater detail below, produces theauxiliary frequency 40, which is designated as C:f_(AFC). Referring toFIG. 7, the frequency response for the auxiliary frequency is shown tohave a substantially lower frequency than the divided frequency 38 orthe reference frequency 32. For this implementation, the auxiliaryfrequency will range from a few kilohertz to a few hundred kilohertz.

Summing module 80 produces the corrected frequency 42, which isdesignated as D:f_(vco)/2+f_(AFC). As shown in FIG. 7, the frequencyresponse of the corrected frequency 42 includes the pulse, whichcorresponds to the ½ VCO frequency plus the AFC frequency and also showsan image tone 152 and a local oscillation feed-through 150. These tonesare generated as a result of mixers 62 through 68 having phase/gainmismatches and DC offset. Since these tones cannot be completelyeliminated because they are too close to the desired frequency, one ofthe functions of the processing module 90 in test mode is to minimizethe impact of the tones 150 and 152.

The output of mixers 94 and 96 produce the local oscillation which isdesigned E:3f_(vco)/2+f_(AFC). The frequency response of the localoscillation is shown in FIG. 7 to include a pulse at the localoscillation which is 1.5 times the voltage controlled oscillationfrequency plus the automatic frequency control frequency plus the imagetone and feed-through tone 150 and 152.

Mixers 110 and 112 mix the summation of the I and Q components of thelocal oscillation with the I and Q components of the local oscillationto produce a base-band signal. The base-band signal is designed as F:DC.Referring to the frequency response for point F, the base-band signal124 and 126 has a pulse at 0 (i.e., at DC), and also includes thereflected images of tones 150 and 152.

The base-band signals 124 and 126 are passed through high-pass filters114 and 116 and then converted to digital signals via ADC's 118 and 120.The resulting digital signal is designated as G:DC. The frequencyresponse for the digital base-band signal is shown in FIG. 7 to includeonly the two tones, 150 and 152.

The processing module 90 is operably coupled to receive the digitalrepresentation of tones 150 and 152 and to produce the frequencycorrection signal 93 to minimize their magnitude. Accordingly, theauxiliary frequency synthesizer 92 may adjust its frequency based on thefrequency correction signal 93 in an iterative manner to determineacceptable levels of the tones and/or the find an optimal frequency atwhich the tones are minimized.

FIG. 8 illustrates a schematic block diagram of an alternateself-correcting local oscillator 160 that includes a processing module162 and memory 164. The processing module 162 may be a single processingdevice or a plurality of processing devices. Such a processing devicemay be a microprocessor, microcontroller, microcomputer, digital signalprocessor, field programmable gate array, programmable logic device,state machine or logic circuitry, and/or any device that manipulatessignals (analog and/or digital) based on operational instructions. Thememory 164 may be a single memory device or a plurality of memorydevices. Such a memory device may be a read-only memory, random accessmemory, volatile memory, non-volatile memory, static memory, dynamicmemory, flash memory, and/or any device that stores digital information.Note that when the processing module 162 implements one or more of itsfunctions via a state machine or logic circuitry, the memory storing thecorresponding operational instructions is embedded within the circuitrycomprising the state machine or logic circuitry. The operationalinstructions stored in memory 164 and executed by processing module 162are generally illustrated in the logic diagrams of FIGS. 9 through 12.

FIG. 9 illustrates a logic diagram of a method for generating aself-correcting local oscillation. The process begins at Step 170 wherea synthesized frequency is generated from a reference frequency. Thismay be done utilizing a digital phase locked loop that up-converts areference frequency, which may be produced by a crystal oscillator, to adesired frequency. For example, if the self-correcting local oscillatoris to be used within a IEEE 802.11a compliant radio receiver ortransmitter, the synthesized frequency would be generated to be ⅔ rds ofthe frequency band indicated by the 802.11a specification.

The process then proceeds to Step 172 where the synthesized frequency isdivided by a divider value to produce a divided frequency. For example,the divider value may be 2 such that the divided frequency has afrequency of ½ the synthesized frequency. In addition, the dividedfrequency may include a phase delay such that an I component and a Qcomponent of the divided frequency are produced. The process thenproceeds to Step 174 where an auxiliary frequency is generated toemulate frequency spectrum errors and/or to provide fine tuning of theresulting local oscillation. The generation of the auxiliary frequencywill be discussed in greater detail with reference to FIG. 10.

The process then proceeds to Step 176 where the auxiliary frequency ismixed with the divided frequency to produce a corrected frequency. Thismay be done by mixing an I component of the auxiliary frequency with a Qcomponent of the divided frequency to produce a 1^(st) mixed frequency;mixing a Q component of the auxiliary frequency with the Q component ofthe divided frequency to produce a 2^(nd) mixed frequency; mixing the Icomponent of the auxiliary frequency with the I component of the dividedfrequency to produce a 3^(rd) mixed frequency; mixing the Q component ofthe auxiliary frequency with the I component of the divided frequency toproduce a 4^(th) mixed frequency; summing the 1^(st) mixed frequencywith the 4^(th) mixed frequency to produce an I component of thecorrected frequency; and summing the 2^(nd) mixed frequency and the3^(rd) mixed frequency to produce an I component of the correctedfrequency.

As an alternative method for producing the corrected frequency, thedivided frequency may be mixed with an I component of the auxiliaryfrequency to produce an I component of a mixed frequency. The dividedfrequency may also be mixed with a Q component of the auxiliaryfrequency to produce a Q component of the mixed frequency. The I and Qcomponents of the mixed frequency may be then filtered by a polyphasefilter to produce an I and Q component of the corrected frequency.

The process then proceeds to Step 178 where the corrected frequency ismixed with the synthesized frequency to produce a local oscillation.

FIG. 10 illustrates a method for generating the auxiliary frequency toprovide fine tuning of the local oscillation. The process begins at Step180 where an I and Q component of the auxiliary frequency are producedbased on a frequency correction signal. The process then proceeds toStep 182 where the frequency of an RF signal is determined. The processthen proceeds to Step 184 where the determined RF frequency is comparedwith the frequency of the local oscillation to produce a differencefrequency. The process then proceeds to Step 186 where the frequencycorrection signal is generated to represent the difference frequency. Assuch, the auxiliary frequency is set to adjust the local oscillation tosubstantially equal the reference frequency and/or to center the localoscillation within a channel within the spectrum represented by thereceived RF signal.

FIG. 11 illustrates a method for generating the frequency correctionsignal during test mode. The process begins at Step 190 where the I andQ components of the local oscillation are summed to produce a summedlocal oscillation. The process then proceeds to Step 192 where thesummed local oscillation is mixed with the I component of the localoscillation to produce a 1^(st) test frequency. The process thenproceeds to Step 194 where the summed local oscillation is mixed withthe Q component of the local oscillation to produce a 2^(nd) testfrequency.

The process then proceeds to Step 196 where a 1^(st) error of frequencycomponent that represents a DC offset within the self-correcting localoscillator is determined based on the 1^(st) and 2^(nd) testfrequencies. The process then proceeds to Step 198 where a 2^(nd) errorcomponent frequency representing an image tone of the self-correctinglocal oscillator is determined based on the 1^(st) and 2^(nd) testfrequencies. The process then proceeds to Step 200 where the frequencycorrection signal is generated to minimize the 1^(st) and 2^(nd) errorfrequencies. This was graphically illustrated with reference to FIGS. 6and 7.

The preceding discussion has presented a method and apparatus forgenerating a self-correcting local oscillation. The self-correctinglocal oscillation includes an auxiliary frequency controller that allowsfor fine tuning of the local oscillation and also includes a test modefor minimizing tones produced by the injection of the auxiliaryfrequency. Accordingly, an accurate and readily changeable localoscillator is achieved that may be particularly useful for IEEE 802.11aapplications. As one of average skill in the art will appreciate, otherembodiments may be derived from the teaching of the present invention,without deviating from the scope of the claims.

1. A self-correcting local oscillator comprises: frequency synthesizerthat generates a synthesized frequency from a reference frequency;divider module operably coupled to divide the synthesized frequency by adivider value to produce a divided frequency; auxiliary frequencycontrol module that generates an auxiliary frequency; first mixingmodule operably coupled to mix the auxiliary frequency with the dividedfrequency to produce a corrected frequency; and second mixing moduleoperably coupled to mix the corrected frequency with the synthesizedfrequency to produce a local oscillation.
 2. The self-correcting localoscillator of claim 1, wherein the divider module further comprises:divide-by-N module that produces an I component of the dividedfrequency; and phase shift module that produces a Q component of thedivided frequency from the I component.
 3. The self-correcting localoscillator of claim 2, wherein the first mixing module furthercomprises: first mixer operably coupled to mix an I component of theauxiliary frequency with the Q component of the divided frequency toproduce a first mixed frequency; second mixer operably coupled to mix aQ component of the auxiliary frequency with the Q component of thedivided frequency to produce a second mixed frequency; third mixeroperably coupled to mix the I component of the auxiliary frequency withthe I component of the divided frequency to produce a third mixedfrequency; fourth mixer operably coupled to mix the Q component of theauxiliary frequency with the I component of the divided frequency toproduce a fourth mixed frequency; first summing module operably coupledto sum the first mixed frequency with and fourth mixed frequency toproduce a Q component of the corrected frequency; and second summingmodule operably coupled to sum the second mixed frequency and the thirdmixed frequency to produce an I component of the corrected frequency. 4.The self-correcting local oscillator of claim 3, wherein the secondmixing module further comprises: fifth mixer operably coupled to mix theQ component of the corrected frequency with the synthesized frequency toproduce a Q component of the local oscillation; and sixth mixer operablycoupled to mix the I component of the corrected frequency with thesynthesized frequency to produce an I component of the localoscillation.
 5. The self-correcting local oscillator of claim 1, whereinthe first mixing module further comprises: first mixer operably coupledto mix the divided frequency with an I component of the auxiliaryfrequency to produce an I component of a mixed frequency; second mixeroperably coupled to mix the divided frequency with an Q component of theauxiliary frequency to produce a Q component of the mixed frequency; andpoly phase filter operably coupled to filter the I and Q components ofthe mixed frequency to produce an I component and a Q component of thecorrected frequency.
 6. The self-correcting local oscillator of claim 1,wherein the auxiliary frequency control module further comprises:auxiliary frequency synthesizer operably coupled to produce an Icomponent and a Q component of the auxiliary frequency based on at leastone of: a frequency correction signal and a fine tuning signal;processing module; and memory operably coupled to the processing module,wherein the memory stores operational instructions that cause theprocessing module to generate the frequency correction signal by:determining frequency of a radio frequency (RF) signal received by aradio receiver that includes the self-correcting local oscillator toproduce a determined RF frequency; comparing the determined RF frequencywith the local oscillation to produce a difference frequency; andgenerating the frequency correction signal to represent the differencefrequency.
 7. The self-correcting local oscillator of claim 6, whereinthe memory further operational instructions that cause the processingmodule to: summing I and Q components of the local oscillation toproduce a summed local oscillation; mixing the summed local oscillationwith the I component of the local oscillation to produce a first testfrequency; mixing the summed local oscillation with the Q component ofthe local oscillation to produce a second test frequency; determining afirst error frequency component that represents a DC offset within theself-correcting local oscillator based on the first and second testfrequencies; determining a second error component freq representing animage tone of the self-correcting local oscillator based on the firstand second test frequencies; and generating the frequency correctionsignal further based on the first and second error frequencies.
 8. Theself-correcting local oscillator of claim 1, wherein the auxiliaryfrequency control module further comprises: auxiliary frequencysynthesizer operably coupled to produce an I component and a Q componentof the auxiliary frequency based on a frequency correction signal;processing module; and memory operably coupled to the processing module,wherein the memory stores operational instructions that cause theprocessing module to generate the frequency correction signal by:summing I and Q components of the local oscillation to produce a summedlocal oscillation; mixing the summed local oscillation with the Icomponent of the local oscillation to produce a first test frequency;mixing the summed local oscillation with the Q component of the localoscillation to produce a second test frequency; determining a firsterror frequency component that represents a DC offset within theself-correcting local oscillator based on the first and second testfrequencies; determining a second error component freq representing animage tone of the self-correcting local oscillator based on the firstand second test frequencies; and generating the frequency correctionsignal based on the first and second error frequencies.
 9. An integratedradio receiver comprises: self-correcting local oscillator thatincludes: frequency synthesizer that generates a synthesized frequencyfrom a reference frequency; divider module operably coupled to dividethe synthesized frequency by a divider value to produce a dividedfrequency; auxiliary frequency control module that generates anauxiliary frequency; first mixing module operably coupled to mix theauxiliary frequency with the divided frequency to produce a correctedfrequency; and second mixing module operably coupled to mix thecorrected frequency with the synthesized frequency to produce a localoscillation; and radio frequency (RF) mixer section operably coupled tomix an inbound RF signal with the local oscillation to produce abaseband signal.
 10. The integrated radio receiver of claim 9, whereinthe divider module further comprises: divide-by-N module that producesan I component of the divided frequency; and phase shift module thatproduces a Q component of the divided frequency from the I component.11. The integrated radio receiver of claim 10, wherein the first mixingmodule further comprises: first mixer operably coupled to mix an Icomponent of the auxiliary frequency with the Q component of the dividedfrequency to produce a first mixed frequency; second mixer operablycoupled to mix a Q component of the auxiliary frequency with the Qcomponent of the divided frequency to produce a second mixed frequency;third mixer operably coupled to mix the I component of the auxiliaryfrequency with the I component of the divided frequency to produce athird mixed frequency; fourth mixer operably coupled to mix the Qcomponent of the auxiliary frequency with the I component of the dividedfrequency to produce a fourth mixed frequency; first summing moduleoperably coupled to sum the first mixed frequency with and fourth mixedfrequency to produce a Q component of the corrected frequency; andsecond summing module operably coupled to sum the second mixed frequencyand the third mixed frequency to produce an I component of the correctedfrequency.
 12. The integrated radio receiver of claim 11, wherein thesecond mixing module further comprises: fifth mixer operably coupled tomix the Q component of the corrected frequency with the synthesizedfrequency to produce a Q component of the local oscillation; and sixthmixer operably coupled to mix the I component of the corrected frequencywith the synthesized frequency to produce an I component of the localoscillation.
 13. The integrated radio receiver of claim 12, wherein theRF mixer section further comprises: seventh mixer operably coupled tomix the Q component of the local oscillation with the inbound RF signalto produce a Q component of the baseband signal; and eighth mixeroperably coupled to mix the I component of the local oscillation withthe inbound RF signal to produce an I component of the baseband signal.14. The integrated radio receiver of claim 13, wherein the RF mixersection further comprises: first high pass filter to filter the Qcomponent of the baseband signal to produce a filtered Q basebandsignal; second high pass filter to filter the I component of thebaseband signal to produce a filtered I baseband signal; first analog todigital converter operably coupled to convert the filtered Q basebandsignal into a digital Q baseband signal; and second analog to digitalconverter operably coupled to convert the filtered I baseband signalinto a digital I baseband signal.
 15. The integrated radio receiver ofclaim 13, wherein the auxiliary frequency control module furthercomprises: auxiliary frequency synthesizer operably coupled to producean I component and a Q component of the auxiliary frequency based on atleast one of: a frequency correction signal and a fine tuning signal;processing module; and memory operably coupled to the processing module,wherein the memory stores operational instructions that cause theprocessing module to generate the frequency correction signal by:determining a difference frequency from the digital I and Q basebandsignals, wherein the difference frequency represents a differencebetween a frequency of the inbound RF signal and the local oscillation;and generating the frequency correction signal to represent thedifference frequency.
 16. The integrated radio receiver of claim 15further comprises: adder operably coupled to sum I and Q components ofthe local oscillation to produce a summed local oscillation; inputselect switch operably coupled provide either the summed localoscillation or the inbound RF signal to the seventh and eighth mixersbased on an input selection signal, wherein, when the input selectswitch provides the summed local oscillation, the eighth mixer mixes thesummed local oscillation with the I component of the local oscillationto produce a first test frequency and the seventh mixer mixes the summedlocal oscillation with the Q component of the local oscillation toproduce a second test frequency; wherein the memory further operationalinstructions that cause the processing module to: determining a firsterror frequency component that represents a DC offset within theself-correcting local oscillator based on the first and second testfrequencies; determining a second error component frequency representingan image tone of the self-correcting local oscillator based on the firstand second test frequencies; and generating the frequency correctionsignal further based on the first and second error frequencies.
 17. Theintegrated radio receiver of claim 13, wherein the auxiliary frequencycontrol module further comprises: auxiliary frequency synthesizeroperably coupled to produce an I component and a Q component of theauxiliary frequency based on a frequency correction signal; processingmodule; and memory operably coupled to the processing module, whereinthe memory stores operational instructions that cause the processingmodule to generate the frequency correction signal by: summing I and Qcomponents of the local oscillation to produce a summed localoscillation; coupling the summed local oscillation to the eighth mixersuch that the eighth mixer mixes the summed local oscillation with the Icomponent of the local oscillation to produce a first test frequency;coupling the summed local oscillation to the seventh mixer such that theseventh mixer mixes the summed local oscillation with the Q component ofthe local oscillation to produce a second test frequency; determining afirst error frequency component that represents a DC offset within theself-correcting local oscillator based on the first and second testfrequencies; determining a second error component freq representing animage tone of the self-correcting local oscillator based on the firstand second test frequencies; and generating the frequency correctionsignal based on the first and second error frequencies.
 18. Theintegrated radio receiver of claim 9, wherein the first mixing modulefurther comprises: first mixer operably coupled to mix the dividedfrequency with an I component of the auxiliary frequency to produce an Icomponent of a mixed frequency; second mixer operably coupled to mix thedivided frequency with an Q component of the auxiliary frequency toproduce a Q component of the mixed frequency; and poly phase filteroperably coupled to filter the I and Q components of the mixed frequencyto produce an I component and a Q component of the corrected frequency.19. A method for generating a self-correcting local oscillation, themethod comprises: generating a synthesized frequency from a referencefrequency; dividing the synthesized frequency by a divider value toproduce a divided frequency; generating an auxiliary frequency; mixingthe auxiliary frequency with the divided frequency to produce acorrected frequency; and mixing the corrected frequency with thesynthesized frequency to produce a local oscillation.
 20. The method ofclaim 19, wherein the dividing the synthesized frequency furthercomprises: dividing the synthesized frequency to produce an I componentof the divided frequency and a Q component of the divided frequency. 21.The method of claim 20, wherein the mixing the auxiliary frequency withthe divided frequency further comprises: mixing an I component of theauxiliary frequency with the Q component of the divided frequency toproduce a first mixed frequency; mixing a Q component of the auxiliaryfrequency with the Q component of the divided frequency to produce asecond mixed frequency; mixing the I component of the auxiliaryfrequency with the I component of the divided frequency to produce athird mixed frequency; mixing the Q component of the auxiliary frequencywith the I component of the divided frequency to produce a fourth mixedfrequency; summing the first mixed frequency with and fourth mixedfrequency to produce a Q component of the corrected frequency; andsumming the second mixed frequency and the third mixed frequency toproduce an I component of the corrected frequency.
 22. The method ofclaim 21, wherein the mixing the corrected frequency with thesynthesized frequency further comprises: mixing the Q component of thecorrected frequency with the synthesized frequency to produce a Qcomponent of the local oscillation; and mixing the I component of thecorrected frequency with the synthesized frequency to produce an Icomponent of the local oscillation.
 23. The method of claim 19, whereinthe mixing the auxiliary frequency with the divided frequency furthercomprises: mixing the divided frequency with an I component of theauxiliary frequency to produce an I component of a mixed frequency;mixing the divided frequency with an Q component of the auxiliaryfrequency to produce a Q component of the mixed frequency; and polyphase filtering the I and Q components of the mixed frequency to producean I component and a Q component of the corrected frequency.
 24. Themethod of claim 19, wherein the generating the auxiliary frequencyfurther comprises: producing an I component and a Q component of theauxiliary frequency based on at least one of: a frequency correctionsignal and a fine tuning signal; determining frequency of a radiofrequency (RF) signal received by a radio receiver that includes theself-correcting local oscillator to produce a determined RF frequency;comparing the determined RF frequency with the local oscillation toproduce a difference frequency; and generating the frequency correctionsignal to represent the difference frequency.
 25. The method of claim24, wherein the generating the frequency correction signal furthercomprises: summing I and Q components of the local oscillation toproduce a summed local oscillation; mixing the summed local oscillationwith the I component of the local oscillation to produce a first testfrequency; mixing the summed local oscillation with the Q component ofthe local oscillation to produce a second test frequency; determining afirst error frequency component that represents a DC offset within theself-correcting local oscillator based on the first and second testfrequencies; determining a second error component frequency representingan image tone of the self-correcting local oscillator based on the firstand second test frequencies; and generating the frequency correctionsignal based on the first and second error frequencies.
 26. The methodof claim 19, wherein the generating of the auxiliary frequency furthercomprises: producing an I component and a Q component of the auxiliaryfrequency based on a frequency correction signal; summing I and Qcomponents of the local oscillation to produce a summed localoscillation; mixing the summed local oscillation with the I component ofthe local oscillation to produce a first test frequency; mixing thesummed local oscillation with the Q component of the local oscillationto produce a second test frequency; determining a first error frequencycomponent that represents a DC offset within the self-correcting localoscillator based on the first and second test frequencies; determining asecond error component freq representing an image tone of theself-correcting local oscillator based on the first and second testfrequencies; and generating the frequency correction signal based on thefirst and second error frequencies.
 27. A self-correcting localoscillator comprises: processing module; and memory operably coupled tothe processing module, wherein the memory includes operationalinstructions that cause the processing module to: generate a synthesizedfrequency from a reference frequency; divide the synthesized frequencyby a divider value to produce a divided frequency; generate an auxiliaryfrequency; mix the auxiliary frequency with the divided frequency toproduce a corrected frequency; and mix the corrected frequency with thesynthesized frequency to produce a local oscillation.
 28. Theself-correcting local oscillator of claim 27, wherein the memory furthercomprises operational instructions that cause the processing module todivide the synthesized frequency by: dividing the synthesized frequencyto produce an I component of the divided frequency and a Q component ofthe divided frequency.
 29. The self-correcting local oscillator of claim28, wherein the memory further comprises operational instructions thatcause the processing module to mix the auxiliary frequency with thedivided frequency by: mixing an I component of the auxiliary frequencywith the Q component of the divided frequency to produce a first mixedfrequency; mixing a Q component of the auxiliary frequency with the Qcomponent of the divided frequency to produce a second mixed frequency;mixing the I component of the auxiliary frequency with the I componentof the divided frequency to produce a third mixed frequency; mixing theQ component of the auxiliary frequency with the I component of thedivided frequency to produce a fourth mixed frequency; summing the firstmixed frequency with and fourth mixed frequency to produce a Q componentof the corrected frequency; and summing the second mixed frequency andthe third mixed frequency to produce an I component of the correctedfrequency.
 30. The self-correcting local oscillator of claim 29, whereinthe memory further comprises operational instructions that cause theprocessing module to mix the corrected frequency with the synthesizedfrequency by: mixing the Q component of the corrected frequency with thesynthesized frequency to produce a Q component of the local oscillation;and mixing the I component of the corrected frequency with thesynthesized frequency to produce an I component of the localoscillation.
 31. The self-correcting local oscillator of claim 27,wherein the memory further comprises operational instructions that causethe processing module to mix the auxiliary frequency with the dividedfrequency by: mixing the divided frequency with an I component of theauxiliary frequency to produce an I component of a mixed frequency;mixing the divided frequency with an Q component of the auxiliaryfrequency to produce a Q component of the mixed frequency; and polyphase filtering the I and Q components of the mixed frequency to producean I component and a Q component of the corrected frequency.
 32. Theself-correcting local oscillator of claim 27, wherein the memory furthercomprises operational instructions that cause the processing module togenerate the auxiliary frequency by: producing an I component and a Qcomponent of the auxiliary frequency based on at least one of: afrequency correction signal and a fine tuning signal; determiningfrequency of a radio frequency (RF) signal received by a radio receiverthat includes the self-correcting local oscillator to produce adetermined RF frequency; comparing the determined RF frequency with thelocal oscillation to produce a difference frequency; and generating thefrequency correction signal to represent the difference frequency. 33.The self-correcting local oscillator of claim 32, wherein the memoryfurther comprises operational instructions that cause the processingmodule to generate the frequency correction signal by: summing I and Qcomponents of the local oscillation to produce a summed localoscillation; mixing the summed local oscillation with the I component ofthe local oscillation to produce a first test frequency; mixing thesummed local oscillation with the Q component of the local oscillationto produce a second test frequency; determining a first error frequencycomponent that represents a DC offset within the self-correcting localoscillator based on the first and second test frequencies; determining asecond error component freq representing an image tone of theself-correcting local oscillator based on the first and second testfrequencies; and generating the frequency correction signal furtherbased on the first and second error frequencies.
 34. The self-correctinglocal oscillator of claim 27, wherein the memory further comprisesoperational instructions that cause the processing module to generate ofthe auxiliary frequency by: producing an I component and a Q componentof the auxiliary frequency based on a frequency correction signal;summing I and Q components of the local oscillation to produce a summedlocal oscillation; mixing the summed local oscillation with the Icomponent of the local oscillation to produce a first test frequency;mixing the summed local oscillation with the Q component of the localoscillation to produce a second test frequency; determining a firsterror frequency component that represents a DC offset within theself-correcting local oscillator based on the first and second testfrequencies; determining a second error component freq representing animage tone of the self-correcting local oscillator based on the firstand second test frequencies; and generating the frequency correctionsignal based on the first and second error frequencies.